Laminated body and manufacturing method thereof

ABSTRACT

A laminated body and fabrication method thereof, which allow space saving and control of variation in internal layer resistance, are provided. When forming an internal-layer resistive element  7  in a multilayer ceramic substrate  10 , the internal-layer resistive element  7  is connected to exterior electrodes (an upper surface electrode  32  and an undersurface electrode  34 ) via multiple via-electrodes  3   a  and  3   b  arranged in parallel, without a pad electrode adopted in the conventional laminated body. Moreover, in a multilayer ceramic substrate having multiple internal-layer resistive elements arranged in a multilayer structure, multiple internal-layer resistive elements are directly connected via multiple via-electrodes arranged in parallel.

TECHNICAL FIELD

The present invention relates to a laminated body, such as a multilayerceramic substrate having internal resistors, for example, and a methodfor manufacturing the same.

BACKGROUND ART

A chip resistor mounted on small electronic equipment etc. has padelectrodes facing each other on an insulating substrate and a resistiveelement bridging between those pad electrodes. In such a resistor, whenthe resistive element is connected to an exterior electrode via a padelectrode, the area of the pad electrode is added to the area of theresistive element in a laminated body. Therefore, for example, a circuitboard having a structure in which a resistive element is formed directlyabove a via-hole without preparing such an electrode, directlyconnecting it to the electric conductor in the via-hole has beenproposed in Japanese Patent Application Laid-Open No. 6-77660.

Since in a conventional chip resistor including a resistive element(resistive layer), a resistance film exposed from the edge face of alaminated insulator has a small area, there is a problem with stabilityof adhesion of the edge face of the resistance film to an exteriorelectrode and lack of reliability of the same. In view of this problem,technology of increasing the exposure area of a resistance film isdisclosed in Japanese Patent Application Laid-Open No. 7-201539.

In the case of the ceramic circuit board disclosed in Japanese PatentApplication Laid-Open No. 6-77660 as described above, electrodes aremade unnecessary so as to allow implementation of a highly dense circuiton a circuit board or miniaturization of the circuit board. However,separately, a terminal for resistance measurement and correspondinginner layer pattern are additionally required. There is thus such aproblem that high density integration is limited. Moreover, since such aconventional ceramic circuit board needs correction of resistance bylaser trimming, a substrate structure in which a resistive element isformed on the top surface of the substrate is employed. There is aproblem that such a structure is inapplicable to a ceramic circuit boardhaving a multilayer resistor structure in which resistive elements arearranged between layers.

On the other hand, according to the chip resistor disclosed in JapanesePatent Application Laid-Open No. 7-201539, connection state between aresistive element and exterior electrodes, that is, connectivity betweena resistance film and an electric conductor section depends upon thecross sectional area of a resistance film, which appears on the edgeface of an insulator. Moreover, there is a limit in increase of the areaof the resistance film because of its properties. As a result,manufacturing of a chip resistor that secures perfect connectivity withan exterior electrode requires advanced manufacturing technology.

The present invention is provided in light of the problems mentionedabove, and aims to provide a laminated ceramic body, which allows spacesaving and controls variation in internal layer resistances, and amanufacturing method thereof.

DISCLOSURE OF INVENTION

In order to attain the aforementioned purpose, the present inventionprovides a laminated body made from multiple laminated green sheets. Thelaminated body is characterized in that it includes an internal-layerresistive element formed inside of the laminated body, an exteriorelectrode arranged on an external end surface of the laminated body, anda first via-electrode, which allows the internal-layer resistive elementto be electrically connected to the exterior electrode, wherein thefirst via-electrode is constituted by multiple via-electrodes arrangedin parallel on one end of the internal-layer resistive element. Thelaminated body according to the present invention is also characterizedin that it further includes a second via-electrode, which allowsconduction of multiple internal-layer resistive elements arranged indifferent layers; wherein the second via-electrode is constituted bymultiple via-electrodes arranged in parallel at the ends of the multipleinternal-layer resistive elements.

Another aspect of the present invention is characterized in that theexterior electrode is arranged on the top surface and the undersurfaceof the laminated body in a lamination direction, and the multiplevia-electrodes include at least two via-electrodes, which are arrangedin parallel and electrically connect one end of the internal-layerresistive element to the exterior electrode arranged on the top surface,and at least two via-electrodes, which are arranged in parallel andelectrically connect the other end of the internal-layer resistiveelement to the exterior electrode arranged on the undersurface.

Yet another aspect of the present invention is characterized in that:the exterior electrode is arranged on the top surface and theundersurface of the laminated body in the lamination direction; theplurality of via-electrodes, which constitute the first via-electrode,comprise at least two via-electrodes arranged in parallel andelectrically connect one end of the internal-layer resistive element tothe exterior electrode arranged on said top surface, and at least twovia-electrodes arranged in parallel and electrically connect the otherend of the internal-layer resistive element to the exterior electrodearranged on said undersurface, and the plurality of via-electrodes,which constitute the second via-electrode, comprise at least twovia-electrodes arranged in parallel and electrically connect ends of theopposing surfaces of the plurality of internal-layer resistive elements,and provide electrical connection between one ends of the opposingsurfaces and between the other ends of the opposing surfaces alternatelyin the lamination direction, according to the lamination structure ofthe plurality of internal-layer resistive elements.

According to the present invention with such a structure describedabove, highly dense assembly and miniaturization (space saving) of alaminated body (multilayer substrate) are possible, and smallervariation in resistance of an internal-layer resistive element may beprovided. Moreover, a ceramic laminated body with improved connectivityof internal resistive elements and exterior electrodes may be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are illustrations showing a structure of a multilayerceramic substrate according to a first embodiment of the presentinvention;

FIG. 2 is a flow chart of a manufacturing process of the multilayerceramic substrate according to the first embodiment of the presentinvention;

FIG. 3 is a perspective outline of the multilayer ceramic substrate,which has resistive elements with a multilayer structure, according tothe first embodiment of the present invention;

FIGS. 4A, 4B, and 4C are sectional drawings showing examples of threedifferent layered structures of a multilayer ceramic substrate accordingto the first embodiment;

FIG. 5 is a graph showing comparison of measurement results of withstandvoltage characteristics of the multilayer ceramic substrate according tothe first embodiment;

FIGS. 6A and 6B are illustrations of constructional examples of amultilayer ceramic substrate, which is constituted by multiple layers,according to a second embodiment of the present invention; and

FIG. 7 is an illustration of a constructional example of a conventionalchip resistor.

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION First Embodiment

Embodiments according to the present invention are described in detailwith reference to attached drawings. FIG. 1A and FIG. 1B areillustrations of a structure of a multilayer ceramic substrate, which isa laminated body, according to a first embodiment of the presentinvention. FIG. 1A is a perspective outline, and FIG. 1B schematicallyillustrates an internal structure of the multilayer ceramic substratewhen seen from above. Here, although multilayer ceramic substrate typesare not limited in particular, they are applicable to, for example, amultilayered circuit board etc. of low temperature co-fired ceramics(LTCC), which is a multilayer ceramic interconnection board with amultilayered circuit pattern in a resistor substrate.

As shown in FIGS. 1A and 1B, with a multilayer ceramic substrate 10according to the first embodiment, a resistive element 7 is arranged ina predetermined layer of the multiple layers comprising the substrate.Multiple via-electrodes 3 a (three electrodes in this case) are arrangedin parallel near an end of the top surface of this resistive element 7,so as to connect an upper electrode 12, which is an exterior electrode,to the resistive element 7 while multiple via-electrodes 3 b arearranged in parallel near the other end of the undersurface of theresistive element 7, so as to secure connection of a lower electrode 14and the resistive element 7. Note that each of the via-electrodes 3 aand 3 b in the multilayer ceramic substrate according to this embodimentmay be constituted by at least two electrodes, so as to improvedefective conduction due to defective via filling.

A manufacturing process for the multilayer ceramic substrate accordingto the first embodiment is described forthwith. FIG. 2 is a flow chartof the manufacturing process of the multilayer ceramic substrateaccording to the first embodiment. In Step S1 of FIG. 2, a ceramicpowder is mixed and ground.

More specifically, a powdered glass, such as a bolosilicate glass, analumina (Al₂O₃) powder and a typical organic vehicle containing abinding agent, a plasticizer, a solvent etc. are mixed, ground,degassed, and thereafter a ceramic green sheet with a specifiedthickness is manufactured using a method, such as the doctor blade(ceramic green tape fabrication). Note that, for example, a mixedsolvent of methyl ethyl ketone and acetone, and polyvinyl butyral resinare used for the above-mentioned organic vehicle.

In Step S3, the ceramic green sheet manufactured in the processmentioned above is cut down to a predetermined size, and a specificsheet is manufactured through each of the following processes. That is,in Step S4, a sheet is manufactured with a through-hole formed using,for example a punch die or a punching machine. Afterward in Step S5, thethrough hole formed in Step S4 described above is filled with aconductive paste of silver (Ag) etc., which is a conductive material.This electric conductive paste has a composition in which silver contentis 85 to 90 percent by weight, silver granules are 3 to 5 micrometers indiameter, and 10 to 15 percent by weight of organic vehicle iscontained, for example.

In Step S6, a sheet including a resistive element is formed. Here, aresistive paste made of a ruthenium oxide material, for example, isprinted using a predetermined printing pattern. This resistive paste ismade with a triple roll mill by dispersing, for example, a rutheniumoxide as a conductive material and glass made from SiO₂, Al₂O₃, BaO, andCaO into a vehicle made from ethyl cellulose and terpineol. Moreover, itis preferable to use an oxide glass, which does not allow excessivesintering of the ceramics around the resistive element or impeding ofsintering, as the glass component of the resistive paste. As such glass,for example, borosilicate barium glass, borosilicate calcium glass,borosilicate barium calcium glass, borosilicate zinc glass, zinc borateglass etc. can be used.

In Step S7, a sheet on which exterior electrodes are printed ismanufactured. More specifically, the sheet on which aforementioned uppersurface electrodes and underside electrodes are formed is manufacturedby screen printing and calcinating a paste of Ag, Ag—Pd etc. on thesheet. Note that these processes of Steps S4 and S5, Step S6, and StepS7 may be carried out either in parallel or serially. In the lattercase, execution order thereof is not limited in particular.

In Step S8, respective green sheets, in each of which a pattern isprinted, resistive elements are formed, and exterior electrodes areprinted as mentioned above, are laminated in a given order. A laminatedceramic green block is then formed by pressure bonding at a pressure of30 Mpa and a temperature of 90° C. through uniaxial pressing, isostaticpressing etc., for example. Afterwards in Step S9, a half-cut is formedalong a cutting line of the block, and in Step S10, debinding andcalcinating are performed at a temperature ranging from 800° C. to 900°C., for example.

FIG. 3 is a perspective outline of a multilayer ceramic substrate havingresistive elements arranged in a multilayer structure, according to thefirst embodiment of the present invention. The multilayer ceramicsubstrate shown in FIG. 3 has a structure made by arranging resistiveelements, which are formed in the multilayer ceramic substrate shown inFIG. 1A and FIG. 1B, in a yet more multilayered structure (in this case,three layers). Therefore, in the multilayer ceramic substrate 20 shownin FIG. 3, resistive elements 27 a, 27 b, and 27 c are arranged in eachof three predetermined layers. In order to connect the resistive element27 a and the upper electrode 32, which is an exterior electrode, threevia-electrodes 23 a are arranged in parallel near one end of the topsurface of the resistive element 27 a located in the upper layer.Moreover, in order to connect the lower electrode 34 and the resistiveelement 27 c, three via-electrodes 23 d are arranged in parallel nearone end of the underside of the resistive element 27 c on the lowerlayer side.

Furthermore, in order to connect the resistive element 27 b located inthe middle layer to each of the resistive elements 27 a and 27 carranged above and below the resistive element 27 b, threevia-electrodes 23 b are arranged in parallel between the resistiveelements 27 a and 27 b, and three via-electrodes 23 c are arranged inparallel between the resistive elements 27 b and 27 c. Morespecifically, the via-electrodes 23 b are arranged in parallel betweenthe undersurface of the opposite side end to the end in which the viaelectrodes 23 a of the resistive element 27 a are arranged and the uppersurface end of the resistive element 27 b while the via-electrodes 23 care arranged in parallel between the undersurface of the opposite sideend to the end in which the via-electrodes 23 b of the resistive element27 b are arranged and the upper surface end of the resistive element 27c. Via-electrodes 23 d are arranged in parallel on the undersurface ofthe opposite side end to the end in which the via-electrodes 23 c arearranged.

Such an arrangement in which via-electrodes are arranged in parallelalternately on the upper surface or the undersurface near the end ofeach of multiple resistive elements arranged in a multilayeredstructure, and the multiple resistive elements are arranged in a rowextends multiple resistive elements in the lamination direction,lengthening dimension L of the resistive elements substantially. As aresult, without lengthening the multilayer ceramic substrate (laminatedbody) more than necessary, the electric strength of the multilayerceramic substrate can be improved as will be described later.

On the other hand, with the conventional chip resistor, electricstrength is improved by lengthening dimension L of a resistive element207 between pad electrodes 205 a and 205 b and thereby making thevoltage per unit length smaller as shown in FIG. 7, for example. Inaddition, in order to improve defective conduction due to defective viafilling, number of each of the via-electrodes 23 a, 23 b, 23 c, and 23 din the ceramic multilayer substrate 20 shown in FIG. 3 is set to atleast two.

Therefore, space saving and cost cutting for such a multilayer ceramicsubstrate having a multilayer structure of two or more layers ispossible by directly connecting an internal-layer resistive element andexterior electrodes via multiple via-electrodes arranged in parallelwithout pad electrodes for forming an internal-layer resistive elementin a substrate. Meanwhile, the same for a multilayer substrate havingmultiple internal-layer resistive elements arranged is also possible bydirectly connecting internal-layer resistive elements via multiplevia-electrodes arranged in parallel. Moreover, precision in resistanceof the resistive elements may be improved because there are no padelectrodes in layers.

Namely, while resistance of the conventional chip resistor varies due topoor printing accuracy of resistive elements and/or pad electrodes, themultilayer ceramic substrate according to this embodiment of the presentinvention has a structure that multiple via-electrodes arranged inparallel are directly connected to an internal-layer resistive element,and thus there is an advantage that precision of the resistance of aresistive element may be improved regardless of printing accuracy.Moreover, when a resistive element is formed in an internal layer,resistance adjustment with laser etc. is impossible. Therefore, byimproving precision of resistance through directly connecting multiplevia-electrodes arranged in parallel to the internal-layer resistiveelement, such a disadvantage may be offset.

Note that while the case where the number of the internal-layerresistive elements on the multilayer ceramic substrate according to theaforementioned embodiment is one or three has been explained, thepresent invention is not limited to that number, and it may be a 2-layerstructure, a 4-layer structure, or a multilayer structure with a largernumber of layers.

Next, electric strength of the multilayer ceramic substrate withmultiple resistive elements serially arranged in a multilayeredstructure is explained. FIGS. 4A to 4C are sectional drawingsillustrating three examples of layered structures of the multilayerceramic substrate according to the first embodiment of the presentinvention. The multilayer ceramic substrate shown in FIG. 4A has twelvelayers of which the middle layer includes a resistive element 47, wherethe resistive element 47 is connected to an upper electrode 42 viamultiple via-electrodes 43 a arranged in parallel and is connected to alower electrode 44 via multiple via-electrodes 43 b similarly arrangedin parallel. Moreover, the multilayer ceramic substrate shown in FIG. 4Bhas a structure in which twelve layers are divided into three equalparts, and resistive elements 57 a and 57 b are arranged between thefourth layer and the fifth layer and between the eighth layer and theninth layer, respectively. The resistive element 57 a is connected to anupper electrode 52 via multiple via-electrodes 53 a arranged inparallel, and the resistive element 57 b is connected to a lowerelectrode 54 via multiple via-electrodes 53 c arranged in parallel.Furthermore, it has a structure in which the resistive element 57 a isconnected to the resistive element 57 b via multiple via-electrodes 53 barranged in parallel.

The multilayer ceramic substrate shown in FIG. 4C has a structure ofthree layers of resistive elements. More specifically, it has astructure in which resistive elements 67 a, 67 b, and 67 c are arrangedbetween the second layer and the third layer from the top, between thesixth layer and the seventh layer, and between the tenth and theeleventh layer, respectively. The upper electrode 62 is connected to theresistive element 67 a via multiple via-electrodes 63 a arranged inparallel, the resistive element 67 a is connected to the resistiveelement 67 b via multiple via-electrodes 63 b arranged in parallel, andthe resistive element 67 b is connected to the resistive element 67 cvia multiple via-electrodes 63 c arranged in parallel. Furthermore, theresistive element 67 c is connected to an undersurface electrode 64 viamultiple via-electrodes 63 d arranged in parallel.

FIG. 5 shows comparison of measurement results in withstand voltagecharacteristics of each multilayer ceramic substrate shown in FIGS. 4Ato 4C. In FIG. 5, the horizontal axis denotes applied voltage (V)between the upper electrode and the lower electrode of the multilayerceramic substrate, and the vertical axis denotes change in resistance

R(%) at each applied voltage. As shown in FIG. 5, the greater the numberof layers of resistive elements arranged in the multilayer ceramicsubstrate, the smaller the change in resistance. That is, such amultilayer structure lengthens dimension L of the resistive elements,and consequently improves the withstand voltage characteristic of theceramic multilayer substrate.

Second Embodiment

A second embodiment according to the present invention is explainedforthwith. FIG. 6A and FIG. 6B show a structure of a multilayer ceramicsubstrate according to a second embodiment of the present invention,wherein FIG. 6A is a perspective outline showing an internal structureof the multilayer ceramic substrate, and FIG. 6B schematically shows aninternal structure of the ceramic multilayer substrate of FIG. 6A whenseen from above.

With the multilayer ceramic substrate shown in FIGS. 6A and 6B, padelectrodes 105 a and 105 b are arranged facing each other on thesubstrate of a predetermined layer comprising a laminated body of aceramic multilayer substrate (laminated body) 100, and a resistiveelement 107 bridges between these pad electrodes 105 a and 105 b.Multiple (three in the case shown in FIGS. 6A and 6B) via-electrodes 103a and 103 b arranged in parallel are arranged on the pad electrodes 105a and 105 b. With such a structure, one ends of the respectivevia-electrodes 103 a and 103 b are connected to the pad electrodes 105 aand 105 b, and the other ends of the same are connected to exteriorelectrodes (upper electrode 102 and lower electrode 104).

As a result, since not only the resistive element 107 is connected tothe exterior electrodes 103 and 104 via multiple via-electrodes 103 aand 103 b arranged in parallel, but also via-electrodes are arranged notcovering the resistive element, there is an advantage that restrictionsby via-electrodes do not adversely affect arrangement of a resistiveelement between layers in a multilayer ceramic substrate comprisingmultiple layers. Furthermore, by arranging multiple via-electrodes inparallel on pad electrodes, which can secure a large area, secureconnectivity of resistive elements to exterior electrodes may beprovided irrelevant of sectional area of a resistance film as that ofthe conventional structure.

INDUSTRIAL APPLICABILITY

According to the laminated body and fabrication method thereof of thepresent invention, highly dense assembly of a laminated body,miniaturization, and space saving are possible. When this is applied tolaminated resistors, variation in resistance can be made smaller, and itis applicable to applications for improved connectivity between theinternal resistive elements and exterior electrodes. Moreover, inaddition to resistors, it is also applicable to multilayer capacitors,inductors etc.

1. A laminated body made from a plurality of laminated green sheets;said laminated body comprising: an internal-layer resistive elementformed inside of the laminated body, an exterior electrode arranged onan external end surface of the laminated body, and a firstvia-electrode, which allows the internal-layer resistive element to beelectrically connected to the exterior electrode, wherein the firstvia-electrode is constituted by a plurality of via-electrodes arrangedin parallel on one end of the internal-layer resistive element.
 2. Thelaminated body according to claim 1, further comprising a secondvia-electrode, which allows conduction of a plurality of internal-layerresistive elements arranged in different layers; wherein the secondvia-electrode is constituted by a plurality of via-electrodes arrangedin parallel at the ends of the plurality of the internal-layer resistiveelements.
 3. The laminated body according to claim 1, wherein theexterior electrode is arranged on the top surface and the undersurfaceof the laminated body in a lamination direction, and the plurality ofvia-electrodes comprises at least two via-electrodes, which are arrangedin parallel and electrically connect one end of the internal-layerresistive element to the exterior electrode arranged on said topsurface, and at least two via-electrodes, which are arranged in paralleland electrically connect the other end of the internal-layer resistiveelement to the exterior electrode arranged on said undersurface.
 4. Thelaminated body according to claim 2, wherein the exterior electrode isarranged on the top surface and the undersurface of the laminated bodyin the lamination direction, the plurality of via-electrodes, whichconstitute the first via-electrode, comprise at least two via-electrodesarranged in parallel and electrically connect one end of theinternal-layer resistive element to the exterior electrode arranged onsaid top surface, and at least two via-electrodes arranged in paralleland electrically connect the other end of the internal-layer resistiveelement to the exterior electrode arranged on said undersurface, and theplurality of via-electrodes, which constitute the second via-electrode,comprise at least two via-electrodes arranged in parallel andelectrically connect ends of the opposing surfaces of the plurality ofinternal-layer resistive elements, and provide electrical connectionbetween one ends of the opposing surfaces and between the other ends ofthe opposing surfaces alternately in the lamination direction, accordingto the lamination structure of the plurality of internal-layer resistiveelements.